PROJECT SUMMARY Streptococcus pyogenes, also known as Group A Streptococcus (GAS), is a gram-positive pathogen that, in its virulent state, is responsible for a variety of human diseases ranging from acute pharyngitis, impetigo, scarlet fever, and necrotizing fasciitis. In addition to its contribution to these disease states, the bacterium is also asymptomatically colonizing up to 35% the population, and this colonization state remains its major reservoir for survival. Our group has characterized a novel quorum sensing system in S. pyogenes termed the Rgg2/3 pathway which consists of two transcriptional regulators, an activator (Rgg2) and a repressor (Rgg3) that are modulated by two short hydrophobic peptide signals (SHPs). The Rgg 2/3 circuit regulates a small secreted protein, Stc, that induces increased biofilm formation and enhanced lysozyme resistance. Both of these phenotypes are indicative of alterations to the cell surface of the bacterium, and we have recently shown that the positively-charged Stc protein is secreted to the cell surface where it associates with surface moieties and makes the surface more positively charged. This proposal seeks to confirm the surface moieties with which Stc associates, and determine whether or not they are obscurred from detection by the host by Stc?s presence. We have preliminary data showing that Stc expression leads to decreased activation of NF?B, which leads us to believe the Stc-expressing bacteria will have a colonization advantage. A murine model of intranasal colonization will be carried out to confirm this colonization advantage as well as examine the NF?B response in vivo. Success of this project work will allow us to explore use of already identified therapeutics that disrupt Rgg2/3 QS in order to eliminate bacteria in a colonizing state.